Hydraulic elevators include a hydraulic jack which is mounted in the hoistway pit and supports the elevator car. A pump unit supplies hydraulic fluid from a reservoir to the jack through a solenoid-operated valve that includes flow regulating pistons for selectively raising and lowering the car. The valve is, in turn, operated by a control system. The control system performs the functions of receiving hall calls and car calls, dispatching the car to the appropriate floors, stopping the car level with the floor landings, and opening and closing the doors. Part of the overall control system is a selector, which senses the position of the elevator car in the hoistway and determines slowdown and stopping points.
Traditionally, all of the control functions of a hydraulic elevator, including those of the selector, have been performed by relay circuitry centrally located in the machine room adjacent to the pump unit. Car position signals are provided by switches mounted at appropriate locations in the hatchway. The switches are actuated by cams mounted on the car and the signals are brought to the controller by a hoistway riser.
Microprocessors possess a number of potential advantages over relay-based controls from the standpoint of system feexibility. It would be desirable, therefore to replace the selector relay controls in a hydraulic elevator with a microprocessor controller, provided that such a control could be employed with hydraulic elevator hardware in a safe and cost effective manner.
As noted before, traditionally the controller and power unit are located in the machine room. The operating temperatures and vibrations of hydraulic elevator machinery make the machine room a reltively inhospitable environment for delicate components such as microprocessors. It is not practical, then, to substitute a microprocessor control for relay circuitry without either taking special protective measures or utilizing components having higher specifications than that of typical industrial or consumer-grade components. This is undesirable from the standpoint of the higher costs involved.
Alternatively, as one manufacture has done, the microprocessor control may be relocated to another location such as on the car. However, the control circuitry in conventional hydraulic elevators is located in the machine room for accessibility and in order to be located close to the power unit, thereby minimizing the amount of power wiring. Relocating the control would require then additional wiring so that the microprocessor will still be able to communicate with the machinery and power supplies in the machine room and switches in the hoistway. To reduce installation cost and to improve reliability it is desirable to keep the amount of wiring to a minimum.
Each microprocessor has inherent limitations in terms of its input/output capabilities (number of I/O ports), processing capability, and speed. In any control system for an elevator, it is undesirable to have delays in processing and transmitting critical information, such as slowdown and stop signals, certain door control signals, and safety information. At the same time, it would be desirable from the standpoint of cost to minimize the number of dedicated terminals used by the central control for input/output with peripheral devices, to perform control functions using minimum microprocessor capability, and to perform critical decision-making functions with a minimum of delay.
As noted above, conventional hydraulic elevator selectors utilize switches mounted in the hoistway. This involves considerable installation costs, but the use of discrete switches for each control signal provides a simple method of outputting car position as a signal suitable for actuating the relay controller. Since each hoistway position requires a discrete switch, it is not practical to mount a corresponding number of separately actuated, discrete switches on the elevator car.
There is, however, an advantage to locating all the active devices in a factory-wired unit mounted on the car, and in using only inert devices in the hoistway.
One known selector system that meets these requirements consists of a tape mounted vertically in the hatch. The tape includes a series of vertically spaced holes, with sensors on the car to detect the holes, and thus count the distance of car travel. The system also includes magnets, mounted on the tape, to indicate floor level, door zone, and to identify each floor by a unique digital code. These magnets are read by separate sensors.
In practice, this system is extremely sensitive to the relative positions of the holes, magnets and sensors, and each must be precisely positioned during elevator setup. In this known system, positioning of the floor magnets and sensors is done on site, on a trial and error basis. This requires a great deal of time in elevator set up and therefore is costly. It also requires the use of personnel having specialized training in the selector system installation procedures.
It would be desirable, in conjunction especially with a microprocessor-based control system, to provide a selector system in which the active components may be mounted on the car, that will provide signals in a form readily adapted for use as microprocessor inputs, but which at the same time may be manufactured on a cost-efficient basis and installed in the field with minimum effort. It would also be desirable to utilize the same selector system to obtain signals representative of the direction of travel. It would further be desirable to minimize the installation time for a tape system employing magnetic sensors, to reduce the cost of elevator installation in the field.